Method and apparatus for manufacturing semiconductor device

ABSTRACT

A method and apparatus for manufacturing a semiconductor device is disclosed. In particular, the application discloses a method that performs a lithography process using a material capable of increasing a depth of focus so as to prevent efficiency of the lithography process from being degraded due to high integration of a semiconductor device, and a pressure-type bake oven as an apparatus for forming a high refractive material on a semiconductor substrate, having advantages of reducing manufacturing costs of a semiconductor manufacturing process and increasing efficiency of the lithography process.

This application is based upon and claims the benefit of priority toKorean Patent Application No. 10-2007-0065546, filed on Jun. 29, 2007,the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The invention relates to a method and apparatus for manufacturing asemiconductor device. In particular, the invention relates to a methodthat performs a lithography process using a high refractive materialcapable of increasing a depth of focus so as to prevent the efficiencyof the lithography process from being degraded due to high integrationof a semiconductor device, and using a pressure-type bake oven as anapparatus for forming a high refractive material on a semiconductorsubstrate. The invention has the advantages of reducing manufacturingcosts of a semiconductor manufacturing process and increasing efficiencyof the lithography process.

BACKGROUND

As the integration of a semiconductor device becomes higher, the size ofthe semiconductor device is reduced, and as a result, a lithographyprocess that is used to manufacture the semiconductor device becomesmore complicated. At present, as an exposure wavelength when a patternof dense lines or a single line is formed, a wavelength of 248 nm or 193nm is mainly used. Recently, patterning that uses a wavelength of 157 nmis gradually being used.

When the shorter wavelength is used, if the structure of a thin film,such as a photoresist, which is formed on a semiconductor substrate, isslightly changed, the resolution and depth of focus (DOF) are decreased.Accordingly, the pattern may be distorted and Line Edge Roughness (LER)may occur.

In a general lithography process, the structure of the photoresist isprimarily changed during a bake process.

FIG. 1 is a cross-sectional view showing a bake oven according to therelated art.

Referring to FIG. 1, the bake oven includes a heating plate 10. Heatrays 20 are provided at an upper portion inside the heating plate 10 toheat a wafer 30, and an exhaust pipe 70, through which a gas 60 isejected, is provided at an edge of the heating plate 10.

A cover 40 is provided above the plate 10, and gas ejection nozzles 50are provided inside the cover 40.

If the wafer 30 is heated using the heat rays 20, it does not heatuniformly over the entire surface. Accordingly, during the bake process,the gas 60 is ejected on the surface of the wafer 30 to disperse theheat.

When the thin film is formed in such a manner, during the bake process,the molecular weight of the thin film is increased by geometricprogression, and the thickness of the thin film is unnecessarilyincreased. Accordingly, the depth of focus (DOF) is changed during anexposure process. As a result, costs for the lithography process areincreased, and the efficiency of the semiconductor manufacturing processis reduced.

SUMMARY

Embodiments consistent with the invention are directed to a method ofmanufacturing a semiconductor device. The method includes forming a thinfilm for a mask pattern on a semiconductor substrate, applying pressureto the thin film so as to improve the density and refractive index ofthe thin film and performing a lithography process on the thin film toobtain the mask pattern.

The thin film may be a photochemical thin film. The pressure may beapplied by pressurizing a gas into a bake apparatus. The temperaturewhen the gas is injected is preferably in the range of about 100° C. to300° C., and more preferably, in the range of about 170° C. to 220° C.Further, the pressure may be applied by irradiating an ultraviolet rayor an electron beam onto the thin film. In addition, the pressure may beapplied by applying a physical force to the thin film. The pressure maybe in the range of about 10 psi to 100 psi. The lithography process maybe an immersion lithography process.

According to another embodiment of the invention, there is provided anapparatus for manufacturing a semiconductor device. The apparatusincludes a heating plate for a bake oven that heats a wafer, a bake ovencover that covers the heating plate, gas nozzles that providing a gasinto the bake oven cover and pressure pumps for pressuring the gasprovided into the gas nozzles.

The heating plate may be an indirect heating-type plate. The gas may beone of nitrogen, helium, argon, and a mixed gas thereof. A primary and asecondary pressure pump are provided for increasing the pressure.Temperature control units are provided among the bake oven cover, theprimary pressure pump, and the secondary pressure pump, respectively.Preferably, when the gas is injected, the temperature control unitpreferably controls a temperature to be in the range of about 100° C. to300° C. More preferably, when the gas is injected, the temperaturecontrol unit controls a temperature to be in the range of about 170° C.to 220° C. The pressure in the bake oven may be in the range of about 10psi to 100 psi.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a bake oven according to therelated art;

FIG. 2 is a conceptual view illustrating Snell's law regarding lightrefraction at a boundary of two mediums having different densitiesaccording to one exemplary embodiment;

FIG. 3 a graph illustrating refraction of a plane wave according to oneexemplary embodiment;

FIGS. 4A and 4B are cross-sectional views showing a difference in lightpath according to a refractive index of a thin film during an immersionlithography process according to one exemplary embodiment;

FIG. 5 is a cross-sectional view showing a change in light pathaccording to a difference in refractive index between thin filmsaccording to one exemplary embodiment; and

FIG. 6 is a cross-sectional view showing a bake oven according to oneexemplary embodiment.

DETAILED DESCRIPTION

Hereinafter, a method and apparatus for manufacturing a semiconductordevice according to an embodiment of the invention will be described indetail with reference to the accompanying drawings.

FIG. 2 is a conceptual view illustrating Snell's law regarding lightrefraction at a boundary of two mediums having different densities.

Referring to FIG. 2, when the refractive index of a first medium is n1,the refractive index of a second medium is n2, the refractive index of athird medium is n3, and angles between light incident on the individualmediums and perpendiculars with respect to individual interfaces betweenthe mediums are θ1, θ2, and θ3, Snell's law is as follows:

When n1<n2,θ1>θ2  (1)

When n₂>n₃,θ₂<θ₃  (2)

That is, when light is incident from the first medium on the secondmedium, reflection and refraction of light occur at the interface. Atthis time, when an angle between the perpendicular of the interface andan incident light beam is θ_(a), and a reflection angle and a refractionangle are θ_(r) and θ_(b), the law of reflection and the law ofrefraction can be obtained as follows according to Huygens' principle:

Law of Reflection

θa=θr (The reflection angle θr is equal to the incident angle θa. Thisrelationship is constantly established regardless of the lightwavelength and the types of the two mediums.)

Law of Refraction

When light is incident on a medium a at an angle of θo in a vacuum, ifthe refractive index of the medium a is na, the following expression isestablished:

sin θo/sin θa=na

This expression is called the law of refraction or Snell's law. Here, iflight is incident on a medium b at an angle of θo in a vacuum, when therefractive index of the medium b is nb, the following expression isestablished:

sin θo/sin θb=nb

From this expression, it can be seen that the expression sin θa/sinθb=nb/na is established.

Accordingly, a relative refractive index n(=nb/na) when light isincident from the medium a on the medium b can be obtained. For example,total internal reflection occurs when light is incident from a mediumhaving a high refractive index on a medium having a low refractive indexand θb=90° (Sin θb=1). And the following relationship is established:

sin θa/sin θb=sin(θa=θc)/sin(θb=90°)=sin θc

If the incident angle θa is equal to or more than the critical angle θc,refracted light disappears, and total internal reflection is made.

FIG. 3 is a graph showing refraction of a plane wave according toHuygens' principle.

Referring to FIG. 3, it can be seen that, since a traveling wave passesthrough two mediums having different densities at different velocities,a wavefront BB′ has a predetermined slope with respect to a wavefrontM′.

Here, when the velocities of the traveling wave in the two mediums arev1 and v2, and the incident angle and the reflection angle are θ1 andθ2, the following relationship is established:

sin θ1/sin θ2=v1/v2

If the lithography process is performed using a hyper-NA (>1.0) lensaccording to Snell's law and Huygens' principle, the incident angle isequal to or more than the critical lens in a projection lens.Accordingly, total internal reflection is made in the lens, and light isnot transmitted to the lower portion of the lens, such that thelithography process may not be performed. For this reason, an immersionlithography process is performed by disposing water having a density(refractive index) higher than air below the projection lens to reduce adifference in density at the interface, and as a result, the lithographyprocess is performed.

FIGS. 4A and 4B are cross-sectional views showing a difference in lightpath according to a refractive index of a thin film during an immersionlithography process.

Referring to FIGS. 4A and 4B, the refractive index of a high refractiveindex fluid 200 is 1.65, the refractive index of a first thin film shownin FIG. 4A is 1.62, and the refractive index of a second thin film shownin FIG. 4B is 1.69.

Accordingly, when light travels from the high refractive index fluid 200as an immersion portion of an immersion lithography apparatus to thethin film 210 or 215, as the refractive index of the thin film 210 or215 is increased, the depth of focus (DOF) is increased.

FIG. 5 is a cross-sectional view showing a change in light pathaccording to a difference in refractive index between thin films.

Referring to FIG. 5, a hard mask layer 230 is provided on asemiconductor substrate 240, and a photoresist 220 is formed on the hardmask layer 230. Next, the high refractive index fluid 200 as theimmersion portion of the immersion lithography apparatus is disposedabove the photoresist 220, and then an exposure process is performed.

At this time, the refractive index of the high refractive index fluid200 is 1.65, the refractive index of each of the photoresist 220 and thehard mask layer 230 is 1.67, and the refractive index of thesemiconductor substrate 240 is 1.25. Since the refractive index of eachof the photoresist 220 and the hard mask layer 230 is higher than thatof the high refractive index fluid 200, the depth of focus (DOF) isincreased to some degree. In this case, however, since the refractiveindex of the semiconductor substrate 240 is low, total internalreflection may occur at the surface of the substrate. Accordingly,efficiency of the lithography process may be degraded. For this reason,there is a need for a method that can increase the refractive index ofeach of the photoresist 220 and the hard mask layer 230.

According to an embodiment of the invention, there is provided a methodthat can increase the refractive index by increasing the density of thethin film when the thin film is formed on the semiconductor substratefor the lithography process. When the thin film is formed, if pressureis applied to the thin film or an ultraviolet ray or an electron beam isirradiated onto the thin film, the density of the thin film can beincreased, and thus the refractive index can be increased.

If the density of a medium, through which light passes, is increased,the traveling velocity of light is decreased. The relationship betweenthe refractive index and the density of the medium also follows Snell'slaw:

n12=v1/v2=sin i/sin r=d2/d1

Here, n12 represents a refractive index when light is incident from aprimary medium on a secondary medium, v1 and v2 represent velocities oflight in the primary medium and the secondary medium, d1 and d2represent densities of the primary medium and the secondary medium, andi and r represent an incident angle and a reflection angle.

From this expression, it can be seen that, if the densities of themediums d1 and d2 are increased, the refractive index n12 is alsoincreased.

When the thin film comprises a photochemical thin film, such as anantireflection film, a photoresist, or a top coating material, the thinfilm is formed on the wafer by a spin coating method, and then pressureis applied during the bake process. At this time, one of nitrogen,helium, argon, and a mixed gas thereof is preferably used.

As the hard mask layer, a thin film containing silicon (Si) and polymeris preferably formed. At this time, any gas can be unlimitedly used toapply pressure.

When the gas is injected into the bake apparatus, the temperature ispreferably maintained in the range of about 100° C. to 300° C., and morepreferably, in the range of about 170° C. to 220° C. In addition, thepressure is in the range of about 10 psi to 100 psi.

Alternatively, a method that increases the density of the thin film bydirectly applying pressure to the thin film after the thin film isformed may be used, without performing the pressure-type bake process.

According to the relationship between volume and pressure as discoveredby Robert Boyle and Jacques-Alexandre-Cesar, the volume of apredetermined amount of gas is inversely proportionate to the pressurewithin the experimental error so long as the temperature remainsconstant.

That is, the product of the pressure and volume of a predeterminedamount of gas is constant when the temperature remains constant.

This is called Boyle's law. Boyle's law can be represented in variousways, but it is formally represented by the following equation:

PV=Constant

Here, P indicates the pressure of a gas having a predetermined mass whentemperature remains constant, and V indicates its volume.

The constant varies the temperature and mass of the gas or the propertyof the gas. The above equation can be represented as follows:

P1V1=P2V2

Here, V1 is the volume of a predetermined amount of gas when thepressure is P1, and V2 is a volume of the gas when the pressure ischanged to P2 at the same temperature. When the volume of a gas at apredetermined pressure is given, the volume of the gas at a differentpressure can be calculated using Boyle's law.

When the pressure and volume of a predetermined amount of low pressuregas within a closed system are P1 and V1, and the volume is V2 when thepressure is changed to P2 at the same temperature, the followingrelationship is established:

P1V1=P2V2

With respect to a change in volume according to a change in temperatureaccording to Charles's law, in case of a gas, the coefficient ofexpansion has no relation to temperature and materials at constantpressure, and the volume of the gas increases by 1/273.15 of its volumeas temperature rises by 1° C.

If the volume of a gas at 0° C. is V0, and the volume thereof at t° C.is Vt, when the condition P=Constant is satisfied, the followingexpression is established:

Vt=V0(1+1/273.15·t)=V0(1+β·t)

Accordingly, if a temperature in a pressure chamber according to anembodiment of the invention increases, a pressure in the chamber, itsvolume remaining unchanged, increases. In addition, the pressure in thechamber, which is maintained at a desired pressure by applying constantpressure, is higher than that at normal temperature. Therefore,according to Blaise Pascal's principle, in hydrodynamics (air orliquid), a change in pressure at a point of the stationary fluid in aclosed container is transferred to other points of the fluid and thewalls of the container with no loss.

The pressure is a value obtained by dividing an applied force by anarea, to which the force is applied. In a hydraulic system, the samepressure as pressure that is applied to a piston is applied to adifferent piston of the system. If the area of the different piston isten times larger than the area of the piston, the pressure that isapplied to the second piston is the same as that of the piston, but theforce increases ten times.

This effect can be observed in a hydraulic press and a hydraulic brakeaccording to Pascal's principle. Further, Pascal has found that pressureto be applied at a point of the stationary fluid is the same in alldirections. That is, the pressure is the same on all planes, which passthrough a predetermined point.

A force that corresponds to the pressure of the pressurized gas isapplied to the wafer in the pressure chamber according to the embodimentof the invention.

According to Pascal's principle, the pressure is transferred to theinner wall of the container, but it can be actually seen that thepressure is applied to all objects, including the pressurized fluid.This phenomenon will be apparent through a submarine balloon experiment.

The submarine balloon experiment may be conducted as follows: a largevolume of container fills with a fluid (water), and a weight suspends asmall balloon at buoyancy such that the balloon stays on the surface ofthe fluid or in the fluid. Next, if the fluid container is closed, andpressure is applied to the fluid, the applied pressure is transferred tothe inner wall of the fluid container by the same force according toPascal's principle. In this case, however, the pressure is applied tothe balloon in the fluid, not the fluid. Accordingly, the balloon isdecreased in size and increased in density, and the buoyancy is removed.As a result, the submarine submerges.

If the pressure applied to the fluid is removed, the submarine risesagain.

As will be apparent from the foregoing experiment, the pressure of thegas applied to the chamber increases pressure by the same force withrespect to the wafer in the chamber, as well as the inner wall of thechamber. If pressure is applied when a spin-coated thin film is dried,the volume of the thin film decreases at the same mass, and its densityincreases. According to Snell's law, the increased density represents ahigh refractive index.

As described above, as a method that forms a thin film having anincreased density, a pressure-type bake method is easily used. A bakeoven for the pressure-type bake method is as follows.

FIG. 6 is a cross-sectional view showing a bake oven according to oneembodiment of the invention.

Referring to FIG. 6, an indirect heating-type plate 300 is provided toheat a wafer 330. A heater 310 is provided in the indirect heating-typeplate 300, and a heating element 320 is provided in the heater 310,thereby uniformly heating the entire surface of the wafer 330.

Next, a bake oven cover 340 is provided to cover the indirectheating-type plate 300. A gas connection pipe 360 is provided at anupper portion of the cover 340, and gas ejection nozzles 350 areprovided inside the upper portion. Accordingly, gas is injected into thebake oven through the connection pipe 360 to increase the pressure inthe bake oven, and thus the density of the thin film that is formed onthe wafer 330 increases.

To increase the pressure using gas, a primary and a secondary pressurepump 380 and 390 are provided. Between the pressure pumps, temperaturecontrol units 370 a, 370 b and 370 c are provided to increase thetemperature of the gas or to cool the gas.

First, the indirect heating-type plate 300 is heated ranging from 100 to300° C., and preferably, ranging from 170 to 220° C., and the pressurein the bake oven is set in the range of about 10 psi to 100 psi usingthe primary pressure pump 380. At this time, since high pressure israrely maintained with only the primary pressure pump 380, pressure thatis 1.2 to 2.5 times higher than the primary pressure is applied by thesecondary pressure pump 390. The temperature control units are used tomaintain the same temperature as the bake temperature.

The refractive index of the resultant thin film can be increased rangingfrom 1.7 to 5, and a fine pattern can be easily formed. In addition,efficiency of the immersion lithography process can be improved.

The embodiment of the invention provides a method that performs alithography process using a high refractive material to thereby increasethe depth of focus (DOF), and a pressure-type bake oven as an apparatusthat forms a high refractive material on a semiconductor substrate.Therefore, costs for a semiconductor manufacturing process can bereduced, and efficiency of the lithography process can be improved. As aresult, efficiency and reliability in manufacturing a semiconductordevice can be improved.

The above embodiments of the invention are illustrative and notlimiting.

The invention is not limited by the type of deposition, etchingpolishing, and patterning steps described herein. Nor is the inventionlimited to any specific type of semiconductor device.

It will be apparent to those skilled in the art that variousmodifications and variations may be made in the present inventionwithout departing from the spirit and scope consistent with theinvention as defined by the appended claims.

1. A method of manufacturing a semiconductor device, the methodcomprising: forming a thin film for a mask pattern on a semiconductorsubstrate; applying pressure to the thin film so as to improve thedensity and refractive index of the thin film; and performing alithography process on the thin film to obtain the mask pattern.
 2. Themethod of claim 1, wherein the thin film comprises a photochemical thinfilm.
 3. The method of claim 1, wherein the pressure is applied bypressurizing a gas into a bake apparatus.
 4. The method of claim 3,wherein, when the gas is injected, the temperature is in the range ofabout 100° C. to 300° C.
 5. The method of claim 3, wherein, when the gasis injected, the temperature is in the range of about 170° C. to 220° C.6. The method of claim 1, wherein the pressure is applied by irradiatingan ultraviolet ray or an electron beam onto the thin film.
 7. The methodof claim 1, wherein the pressure is applied by applying a physical forceto the thin film.
 8. The method of claim 1, wherein the pressure is inthe range of about 10 psi to 100 psi.
 9. The method of claim 1, whereinthe lithography process comprises an immersion lithography process.10-18. (canceled)